A research team from Japan’s National Astronomical Observatory (NAOJ) has raised concerns regarding the accuracy of the widely celebrated image of the supermassive black hole at the center of the Milky Way. The original photograph of Sagittarius A* was produced using data collected by the Event Horizon Telescope (EHT) Collaboration and was unveiled to the public in May 2022. It portrayed the galaxy’s central black hole as a dark cloud encircled by a luminous ring, known as the accretion disk. However, the new paper by the NAOJ team suggests that the accretion disk might be elongated rather than circular. This proposed black hole structure has been published in the Monthly Notices of the Royal Astronomical Society.
The 2022 image captures Sagittarius A*, a massive black hole with a mass equivalent to four million suns, and it represented the first time this object at the galaxy’s core was photographed. It marked the second black hole image produced by the EHT, following the first-ever black hole image, which depicted Messier 87 (M87) and was released in 2019.
Black holes are regions in spacetime where gravity is so strong that nothing, not even light, can escape beyond a certain boundary known as the event horizon. Surrounding this boundary is the accretion disk made of superheated matter. The recent study speculates that the shape of the accretion disk of Sagittarius A* differs from previous interpretations.
The EHT is an extensive radio observatory comprised of a network of telescopes, which captures the silhouette of a black hole—an otherwise invisible object—against its bright accretion disk. Miyoshi Makoto, an astronomer at NAOJ and co-author of the study, stated that errors in the EHT’s imaging analysis could have resulted in an artefactual ring image, rather than depicting the true astronomical structure.
The researchers examined the same 2017 data set used by the EHT Collaboration but employed a different analytical method. This alternative analysis points to an elongated accretion disk rather than the ring-like structure seen in the 2022 image.
The NAOJ team contends that the M87 black hole also exhibits a ring-like appearance in EHT images, which a subsequent team developed into a polarized version that reveals its magnetic fields’ structure. In August, the EHT introduced a new technique to enhance the telescope’s resolution, promising sharper future black hole images. Such advancements could potentially verify the actual configuration of Sagittarius A* in forthcoming observations.
Future prospects may include a space-based mission aimed at refining EHT image resolution further. Estimated to cost $300 million, this “Event Horizon Explorer” mission would investigate black holes’ photon rings, advancing understanding of the universe’s most extreme environments, such as those involving black holes, neutron stars, and their collisions. These insights may enhance knowledge of gravitational processes and the core of the Milky Way.